The late night Prom has become a vessel for experimental, relaxed, often refreshing concerts; programmes that are often a specialised or what you might call "a bit different". The Aurora Orchestra brought all of those things to the Royal Albert Hall on Saturday night. The heavy Mahler of the evening's earlier concert had been swept from the air. It was replaced by infectious energy from a band of musicians who breezed through a diverse and challenging programme without music stands or chairs.

As ever with Proms, it was a high quality concert comprised of two vastly different halves – though there was no interval. The notable anomaly was the second of the three pieces: a duet for hurdy-gurdy and violin that harked back to a bygone storytelling era, whilst keeping some modern bite in its harmonies. The violin took the role of singer, weaving its sound into the drone of the hurdy-gurdy as it churned through a song with no words. It was a curious, endearing piece and well executed. But it was somewhat incongruous with what came before and after.

The opener was Mozart's Symphony no. 40 in G minor, played from memory. Free from music stands and all standing up, Aurora delivered an intensely physical performance. Conductor Nicholas Collon was almost a spare part, such was the level of listening on display, although he did marshall in some pleasingly emphasised dynamics and mood changes. The first movement, a Molto allegro with an instantly recognisable melody that tentatively leans into itself, achieved brilliant contrasts of dynamic and textural depth, giving the familiar work some unpredictability. The difficulty of performing from memory was most obvious in final Allegro assai, a pacy finale played with precision. The Symphony, one of Mozart's last, is infused with the composer's operatic writing and is full of character, and the resulting drama and momentum were beautifully interpreted.

But the real talking point of the concert came when the choir "Chantage" joined an expanded Aurora for the world première of Benedict Mason's Meld. From a composer known for breaking convention, it was never going to be predictable. The work seemed designed to "melt" into the concert hall itself. It's a mad combination of note patterns - random-sounding but requiring spot-on timing - and choreography that saw the musicians scattered and moving around the arena. After two initial groups processed on to the gallery, a guerilla approach to orchestral playing took hold. Small clusters popped up all around the Hall before moving on to another place, another motif. It was an incessant sequence of sounds and formations that blended into one long melee.

When I say long, I mean 45 minutes, which seemed longer because of the fluid, undefined structure. But there were many surprises, particularly an exciting range of percussion, from steel pans to cowbells to a device that made clicking noises. Several moments clearly caught the audience's attention, raising laughs. For example, a Mexican wave effect of instruments rapidly passed notes around and back again, literally creating surround sound – a circular scale around the room. A few singers bowling balls around the arena led to more performers joining them for an elaborate stepping routine, almost a dance, before a sort of climax arrived – brass instruments firing notes at each other – and then the scattered groups of the orchestra departed as suddenly they'd come in. It was only when the entire orchestra assembled to take their bows that the scale of the complex performance became apparent: it involved around 150 performers.

What was it all about? Not an unreasonable question, but you'd probably be wrong to look for a story or a plot. Even the monosyllables sung staccato-style by Chantage were unintelligible. The composer blurrred the line between music and performance art, sometimes poking fun at the structured expectations of a concert hall, sometimes exploring the effects that can be achieved when the musicians are moving about. It was as physical and visual as it was audial. I'm not sure how much it will have made sense to BBC Radio 3 listeners, but in the flesh it was a unique experience which appeared to be flawlessly executed.

The work is proudly original and an impressive achievement – after the concert, Aurora lead cellist Oliver Coates took to Twitter to describe the composer as a "genius" – but it does need an open-minded audience; an audience prepared to be challenged. This was an eclectic performance which came together like a dream.